Re: Installing a resistor on the Map Lights Need Help!
For what it is worth leds are low voltage items. Red is about 2.2 volts per led, green is higher at about 3.5 volts and white which is really red/blue/ green in one package needs about 4.5 volts to light. Blue lights at about 4.5 volts.
Leds draw about 0.020 up to about 0.08 amps per bulb depending on the intensity. Some packaged leds are an array and can draw the sum of all the parts. If there are several in a string they have the same current going thru the string - and the voltage drops are added up. Thus 3 red leds draw about 2.2 volts each or 6.6 volts (for the string example) to light and have a demand of current of about 0.02 or higher current depending on the capacity
Most car lights are a string with a current limiting resistor. As the led wants to see some voltage to light, they do not allow more voltage drop without overheating and shorting into a blown led. The series limiting resistor DROPS or wastes the excess voltage and allows their operation over the varying voltage within our automobile systems.
If the example of three leds are used and the car is at a nominal of 13.2 volts, the dropping resistor would have to drop 6.6 volts and at 0.020 amps the resistor would be 6.6/0.020 or 330 ohms. The resistors heating would be 6.6 volts x 0.020 amps or about 132milliwatts or 0.132 watts of power. Not enough to warm your fingers. 0.020 amps of current is very low power led, like the one that shows you your tv or audio system is on.
A Maglight has about a 3 watt led and for 2 cell operation they draw about a full AMP of current to light the yellow led array at the end of the flashlight.
More trivia......Why do they call it a flashlight?????????????
Way back when the battery was so weak that you flashed it on to see and did not leave the light on, thats why they had the little button to blink or flash it on..like a strobe. How we have grown.
Woody Enjoy.